As is well known, an electric power converter to be mounted in a vehicle or the like is provided with an inverter circuit that performs DC/Ac electric-power conversion between a DC power source such as a vehicle battery and an AC rotating machine for driving a vehicle or the like. This inverter circuit is configured with a plurality of switching devices that are each formed of a power semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor); in general, along with respective free-wheel diodes connected in parallel therewith, these switching devices are mounted on a first circuit provided on a first side of an insulated substrate (e.g., a side that is, in general, referred to as the “top side” or the “front side” of an insulated substrate).
The insulated substrate has the first circuit connected with the switching devices and the free-wheel diodes and a second circuit provided on a second side (e.g., a side that is, in general, referred to as the “bottom side” or the “rear side” of an insulated substrate), which is the side opposite to the first side. In general, the switching devices, the free-wheel diodes, and the insulated substrate are integrally molded with a resin and are provided as a monolithic component, which is referred to as a so-called power module.
In general, with regard to the foregoing power module, the second circuit on the insulated substrate is bonded to a first side of a metal base (e.g., a side that is, in general, referred to as the “top side” or the “front side” of a metal base) through the intermediary of a bonding layer formed through soldering or the like. A fin enclosed with a cover is provided on a second side, which is the side opposite to the first side, of the metal base (e.g., a side that is, in general, referred to as the “bottom side” or the “rear side” of a metal base); while making direct contact with a cooling fluid such as water that flows in the cover, the fin is cooled. As a result, the thermal resistance of a heat conductive path departing from the switching devices and the free-wheel diodes, which are heating elements, and reaching the cooling fluid by way of the metal base and the fin is reduced.
In an electric power converter disclosed in Patent Document 1, the second circuit that has been provided on the second side of the insulated substrate in the power module is omitted and the insulated substrate is bonded to a low-rigidity and soft metal base with a fin, so that the thermal resistance is reduced and the high reliability is obtained.